• Journal of the Korean Society of Industry Convergence
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• v.13 no.2
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• pp.99-106
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• 2010

The effects of additive and shrinkage reducing agent on the drying and autogenous shrinkage of high strength concrete are investigated in this study. As results, when the ratio of W/B(low water to binder ratio) increase, the compressive strength is decreased. Comparing with PC(portland cement) concrete, the strength is 2.8%, 3.2% and 3.8% lower respectively than that of PC when concrete mixing ratio is 0.2%, 0.3% and 0.4% in 28 days curing. Drying shrinkage strain of PC concrete showed $-650{\times}10^{-6}$ in 91 days curing. When SR(shrinkage reducing agent) of 0.2%, 0.3% and 0.4% is mixed, the drying shrinkage strains are 21%, 34% and 41% lower than those of PC in 91 days curing. Autogenous shrinkage strain of PC concrete appeared $-480{\times}10^{-6}$ in 56 days curing. When SR of 0.2%, 0.3% and 0.4% is mixed, the autogenous drying shrinkage strain are 12.5%, 19.8% and 33.3% lower than those of PC in 56 days curing. In cases of using the mineral and shrinkage agent or only using a shrinkage reducing agent also appeared same reducing effects for drying shrinkage and autogenous shrinkage.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2003.10a
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• pp.134-138
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• 2003

The purpose of this paper is to recycle the fly ash to the valuable resources and settle environment problems which was caused by the fly ash produced from the thermal power plant. Making the fly ash-cement matrix reused fly ash in large quantities, we looked into minutely the physical properties - the elastic modulus, the compressive strength - to increase the usefulness as the building materials for the structure widely. In this paper, the variables are the water-binder(39, 42, 45%), the fine aggregate ratio(37, 41, 45%). Because the fracture energy is influenced by the strength, it is showed to decrease with the increase of W/B and S/a. Besides, we will be able to know that basic properties of the fly ash-cement matrix are similar to that of concrete. But, it is needed to carry out durability experiment on the drying shrinkage, creep, freezing and thawing test to use structural materials.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.1-9
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• 2014

In this paper, $CO_2$ amount is evaluated considering repairing timing and unit $CO_2$ amount per repair method including various stage of material manufacturing, moving, and construction. Four mix proportions with mineral admixture are considered and repairing timing/numbers are simulated based on the results from Life 365 which can handle chloride penetration. Furthermore two repair methods (simple cover concrete replacement and replacement with electro-chemical method for removing chloride content) are considered and the related $CO_2$ emissions are evaluated. From the study, the case with high W/B (water to binder ratio) ratio shows smaller $CO_2$ emission in construction stage but it increases more rapidly with increasing number of repair. $CO_2$ emission considering electro-chemical method greatly increases with the increasing unit $CO_2$ for the repairing method. The numbers of jumping step (repairing number) are evaluated to be 9 for WB37-OPC, 18 for WB50-OPC, 4 for WB40-SG, and 7 for WB47-SG respectively. RC structures with the longer maintenance free period are evaluated to be advantageous for saving $CO_2$ emission.

• Computers and Concrete
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• v.17 no.5
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• pp.629-638
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• 2016

Optimization of the concrete mixture design is a process of search for a mixture for which the sum of the cost of the ingredients is the lowest, yet satisfying the required performance of concrete. In this study, a statistical model was carried out to model a cost effective optimal mix proportioning of high strength self-compacting concrete (HSSCC) using the Response Surface Methodology (RSM). The effect of five key mixture parameters such as water-binder ratio, cement content, fine aggregate percentage, fly ash content and superplasticizer content on the properties and performance of HSSCC like compressive strength, passing ability, segregation resistance and manufacturing cost were investigated. To demonstrate the responses of model in quadratic manner Central Composite Design (CCD) was chosen. The statistical model showed the adjusted correlation coefficient R2adj values were 92.55%, 93.49%, 92.33%, and 100% for each performance which establish the adequacy of the model. The optimum combination was determined to be $439.4kg/m^3$ cement content, 35.5% W/B ratio, 50.0% fine aggregate, $49.85kg/m^3$ fly ash, and $7.76kg/m^3$ superplasticizer within the interest region using desirability function. Finally, it is concluded that multiobjective optimization method based on desirability function of the proposed response model offers an efficient approach regarding the HSSCC mixture optimization.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.9-17
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• 2019

Cement hydrates and the related characteristics change with ages, and the behaviors are much related with chloride diffusion. In this work, 30% replacement ratio with FA(Fly Ash) and GGBFS(Ground Granulated Blast Furnace Slag) are considered for concrete with three levels of W/B (Water to Binder ratio) and 2 years of curing period. Chloride diffusion coefficients from accelerated condition are obtained at 5 measurement period (28days, 56days, 180days, 365days, and 730days), and the results are compared with porosity, binding capacity, and permeability from program-DUCOM. The similar changing pattern between chloride diffusion and permeability is observed since permeability is proportional to the square of porosity. Curing period is grouped into 4 periods and the changing ratios are investigated. Cement hydrate characteristics such as porosity, permeability, and diffusion coefficient are dominantly changed at the early ages (28~56 days), and diffusion coefficient in OPC concrete with low W/B continuously changes to 180days.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.421-424
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• 2008

The purpose of this experimental research is to investigate the influence of cement types on the resistance to acid and sulfate. For this purpose, concrete specimens with three types of cement such as ordinary portland cement(OPC), binary blended cement(BBC), and ternary blended cement(TBC) were made for water-binder(W/B) ratios of 32% and 43%, and then according to JSTM C 7401, the appearance change and ratio of mass change of them were estimated through the immersion tests by 5% sulfuric acid, 10% sodium sulfate, and 10% magnesium sulfate solution, respectively. It was observed from the test result that the resistance against acid and sulfate increased with decreasing W/B ratio and those of BBC and TBC concretes were better than the case of OPC concrete from immersion tests of 91 days.

• Journal of the Korea Institute of Building Construction
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• v.22 no.3
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• pp.229-237
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• 2022

Ultra High Performance Concrete(UHPC) is a construction material that has a low water-binder ratio (W/B), a high-performance chemical admixture(SP), mixing material and steel fiber, and performance superior to that of regular concrete in terms of liquidity and strength. In the study, UHPC was used to prepare construction external panels that can replace existing stone panels. In addition, experiments were conducted to access the effects of differences in chemical admixture input amount, the number of fillers, antifoaming agent and steel fiber. An evaluation, was conducted, such of concrete compressive strength, flexural strength, impact strength, absorption rate, and frost resistance. The results showed compressive strength up to 115.5MPa, flexural strength of 20.3MPa, and an absorption rate of 1%. In this case, impact strength and frost resistance evaluation were satisfied with outward observed.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.307-314
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• 2017

Concrete is a durable and cost-benefit construction material, however performance degradation occurs due to steel corrosion exposed to chloride attack. Penetration of chloride ion usually decreases due to hydrates formation and reduction of pores, and the reduced chloride behavior is considered through decreasing diffusion coefficient with time. In the work, HPC (High Performance Concrete) samples are prepared with 3 levels of W/B (water to binder) ratios of 0.37, 0.42, and 0.27 and 3 levels of replacement ratios of 0%, 30% and 50%. Several tests containing chloride diffusion coefficient, passed charge, and compressive strength are performed considering age effect of 28 days and 180 days. Chloride diffusion is more reduced in OPC concrete with lower W/B ratio and GGBFS concrete with 50% replacement ratio shows significant reduction of chloride diffusion in higher W/B ratio. At the age of 28 days, GGBFS concrete with 50% replacement ratio shows more rapid reduction of chloride diffusion than strength development, which reveals that abundant GGBFS replacement has effective resistance to chloride penetration even in the early-aged condition.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.4
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• pp.115-122
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• 2008

This paper is to investigate the affecting factors on spalling of the high strength concrete including W/B, air content and moisture condition as well as PP fiber contents subjected to fire. An increase with 0.05% of PP fiber resulted in a reduction of slump flow by as much as 11%. Ten percent of air contents due to excessive amounts of AE agent does not lead to variance of slump flow, regardless of PP fiber content. For the effect of the compressive strength, high strength concrete with 15, 25 and 35% of W/B gained 60 MPa~100 MPa of the compressive strength. High strength concrete with H-air had half of compressive strength of that with L-air due to large amount of air. Fire test was conducted in accordance with KS F 2257-1 for 1 hour. Spalling did not occur with all specimens containing more than 0.10% of PP fiber except those with 15% of W/B. Moreover, it is interesting to note that the specimens with more than 10% of air content and with oven dried condition, respectively, had no spalling even if the content of PP fiber is 0.05 vol.%.